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arXiv 1108.2647quant-phcond-mat.mes-hallcond-mat.str-el
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非局部酉运算的Ancilla辅助序列逼近

Ancilla-assisted sequential approximation of nonlocal unitary operations

Hamed Saberi

摘要:

我们认为最近提出的“不去”定理的Lamata等人[物理评论快报。101,180506(2008)]关于不可能借助于巡回辅助系统顺序实现全球单一操作,并在Kraus表示的语言内查看该主张。借助一个非常有用的工具来分析量子操作的纠缠特性,即算符施密特分解,我们提供了另一种证明的“不去”定理,也研究了量子比特和附属物之间的初始相关性的作用,在顺序制备幺正纠缠。尽管从“不去”定理的负面反应,我们明确展示了矩阵乘积算子(MPO)的形式主义如何提供了一个灵活的结构,以开发协议,顺序实现这种纠缠与最佳保真度。建议的数值技术,我们称之为变分矩阵乘积算子(VMPO),提供了一个计算效率高的工具,用于表征非局部酉操作的“全局性”和纠缠能力。

英文摘要:

We consider the recently proposed "no-go" theorem of Lamata et al [Phys. Rev. Lett. 101, 180506 (2008)] on the impossibility of sequential implementation of global unitary operations with the aid of an itinerant ancillary system and view the claim within the language of Kraus representation. By virtue of an extremely useful tool for analyzing entanglement properties of quantum operations, namely, operator-Schmidt decomposition, we provide alternative proof to the "no-go" theorem and also study the role of initial correlations between the qubits and ancilla in sequential preparation of unitary entanglers. Despite the negative response from the "no-go" theorem, we demonstrate explicitly how the matrix-product operator(MPO) formalism provides a flexible structure to develop protocols for sequential implementation of such entanglers with an optimal fidelity. The proposed numerical technique, that we call variational matrix-product operator (VMPO), offers a computationally efficient tool for characterizing the "globalness" and entangling capabilities of nonlocal unitary operations.

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